Rear gear selection - Page 3

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  1. #31

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    Originally you were describing the phenomena as;

    Quote Originally Posted by CrucialProspect View Post
    ...it’s not a bog similar to a clutch drop at 6k rpm in a Toyota Corolla on slicks, It just seems to struggle between the power of the engine and the traction at the ground.

    Later in Post #30 you describe it as,

    Quote Originally Posted by CrucialProspect View Post
    Engine rpm and vehicle speed probably isn’t correct. Running 1/8th mile, at a 6500rpm shift point I just shift into 3rd. But upping the shift rpm to 7500 I would be gaining 1000rpm in 1st gear, and 1000rpm in second.

    Those two operating characteristics are unrelated.

    If you are running a manual transmission car with a tall first gear and low on power, engine speed will decrease after the launch because the clutch initially slips at engagement and then as it locks up it pulls the engine down to the rpm that the vehicle speed requires in first gear with the transmission ratio, tire size and rear end ratio the car has.

    If you are running an auto with a stall converter the car will launch with the engine at the converter stall speed, whatever that might be. If the overall first gear ratio, the vehicle weight and the engine power are properly matched the engine will race up its operable rpm range. If you have a first gear ratio that is too tall for the engine to rapidly progress up in rpm, then the engine will labor at the converter stall speed until the vehicle speed and engine speed equalize for that particular gear selection. After the two have equalized the engine will proceed up the rpm band at a rate consistent with its power level and the weight of the car it is pulling.

    This is not complicated stuff. If you look at a data log for a Powerglide car the phenomena jumps out at you because there is only 2 speeds. The car will launch at whatever the converter stall is and "ride" the converter out, going down track, until vehicle speed and engine speed equalize. The engine will rapidly climb to the shift point, a gear change will occur and then the process begins anew as the car heads for the quarter mile clocks.

    You need more boost.



    Ed

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  3. #32

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    If I’m reading correctly, there is no way this car is gonna go faster than [email protected] as it sits, I can handle the truth.

  4. #33

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    More boost ...


    Ed

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  6. #34

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    More Boost... =)

    ks

  7. #35

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    Fellas, give me a break! I have the most complicated over engineered electronic boost gauge imaginable. It will take me a week on the dyno to get the darn thing to build more boost.

    The greddy profec b spec 2 is about the worst thing possible to use, trust me. It took 3 hours to set it to operate of the wastegate and at 15psi.

    Unless anyone can recommend a “user friendly” controller, this is going to take dyno time/waste test and tune at the strip.

    I can tell you this about the system... peak is “I dunno” and you’d think value of 0 is off the gate spring pressure, but it isn’t.... so you enter a percentage that may be your lucky number or lottery ticket go-to pick, and see what pressure pops up on your gauge. Then you have to set the “set gain” and other settings that also affect your total boost, so in all actuality your floating around 3 or 4 values each changing itself.

  8. #36

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    If you want to try a manual controller I used a TurboXS on my GN and I ran it at 35psi and had great results with it. These run just under $100.
    To speed up spool time I used a hobs switch and a relay feeding to the controller. The hobs/relay prevented boost pressure getting to the controller so the controller wouldn't bleed off boost prematurely while building boost. I don't think the hobs/relay is needed in your case, tho.

    ks
    Last edited by KEVINS; 05-28-2020 at 07:26 AM.

  9. #37

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    Sometimes a less sophisticated manual approach like Kevin is suggesting not only works better but is easier to work with.


    Ed

  10. #38

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    I actually want to look into that, seems simple.
    Twist knob, watch gauge. They even have dual stage setup which I believe is what Kevin was describing.

  11. #39

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    I guess the general consensus is to put in wastegate springs that are at your minimum boost levels as the controllers can only be adjusted to about 200%

    If I put in a 15psi spring I should be capable up to 30psi, starting conservative though I’ll shoot for 20psi. Also, their dual system is exactly what Kevin stated, just a solenoid that bypasses the 1st controller and that can be triggered by switch or other means.

  12. #40

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    I think you will find 18 to 20 psi of boost will be a mind expanding experience, Matt. A you already know, the power that is lost to belt driven blowers in that boost range goes directly to the tires on turbo cars. An 18 psi or slightly higher boost level at launch will make a stunning difference in how the car leaves the mark.


    Ed

  13. #41

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    Just a note for the mind closet: I installed WG springs that "calculated" to be 15psi but I actually get 17.5 psi on just the springs so this is the minimum amount I can run if I desire. As you know I have it tuned to 32psi.

    ks

  14. #42

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    Quote Originally Posted by KEVINS View Post
    Just a note for the mind closet: I installed WG springs that "calculated" to be 15psi but I actually get 17.5 psi on just the springs so this is the minimum amount I can run if I desire. As you know I have it tuned to 32psi.

    ks
    Yes, we ran mine on the springs and got a few psi less, it’s hard to remember back that long but they were 10lb springs but only made 8 psi.

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